I'm sure these stability maps exist, but i've never seen them. I think someone from the team will answer you better about it (as they should have those maps), but in the mean time something about Venice:
You are a Merchant Republic, so if you intend to keep it that way be sure not to overexpand, even on Solid or OK provinces. Verona (capital), Tuscany, Croatia and Dalmatia are your Solid provinces. To complete UHV1 you need all of these besides Tuscany.
Your OK provinces are Epirus, Morea, Carinthia, Crete, Rhodes and Constantinople. Epirus is needed for UHV1 and Constantinople for UHV2. If you have only one city in each of the needed provinces, you'll end up with 5 cities. You'll even imagine that everything is fine and your Stability is high, but it's not like this. The last thing you need is to secure an Atlantic Resource (by conquest or by trade). Better by trade, but it's too hard (I think that the only way to do it is trading with a Vassal, nobody else will trade that with you). So a conquest may be needed.
After you get your 6th city things start to be messy (a lot less now in RFCE 1.0, but still considerable). Merchant Republic suffers instability after you get more then 5 cities.
I ended my Venetian game with a Historical Victory having Tuscany, Verona, Croatia, Dalmatia, Epirus, Morea, Crete, Rhodes, Constantinople and Tetouan (Tanjah). Lots of Golden Ages to achieve stability enough for all of them, and Rhodes I only got in the last turn (it wasn't possible for my stability to get it earlier), and Tanjah was for my Atlantic Resource.
Best tip for Venetian game: You MUST control the crusades, all of them, do it everywhere, vassalize some, destroy others, get Jerusalem once (Golden Age), get Constantinople (UHV2 + UHV1 = Golden Age), and best of all: Free units for the Merchant Republic.
This is what I've achieved:
Ended: 1556 AD
Vassals: Portugal, Spain and Austria